We have developed a technique for continuously releasing large molecules such as proteins from non-inflammatory polymeric surgical implants. This technique has been used in several bioengineering studies. In vitro tests have demonstrated sustained release of enzymes, DNA, and insulin for several months. The polymers have been employed in the development of in vivo corneal bioassays for factors isolated from tumors, cartilage and vitreous. Preliminary studies indicate that polymers containing insulin will lower the blood glucose levels in diabetic rats. We propose (1) to investigate the mechanism of release and characterize the release properties of the sustained release polymer systems. Kinetic, microscopic and in vivo studies will be conducted to achieve this objective. (2) to develop a theoretical and experimental framework for achieving zero-order release kinetics (3) explore the feasibility of developing modulated delivery systems. Long range goals include applying the understanding developed in the first three objectives to several important applications of these delivery systems. These applications include (a) to utilize the polymers in the development of controlled delivery systems for clinically and biol gically useful macromolecules; (b) utilizing the polymer to develop a simple one-step method for immunization.